1. Field of the Invention
The present invention relates to a technology for manufacturing a piezoelectric resonator made of, for instance, quartz crystal or the like.
2. Description of the Related Art
The tuning fork type quartz resonator has long been adopted as a signal source for pacing a wrist watch owing to its being compact, inexpensive and having a low power consumption, and the uses thereof are still expanding. Recently, the CI (crystal impedance) value of this quartz resonator is required to be as small as possible, and a quartz resonator with a groove formed therein has been used for this purpose.
The tuning fork type quartz resonator 100 is provided with a base 1 and a pair of vibrating arms 2a and 2b arranged in the base 1, as shown in FIG. 7. Grooves 31 and 32 are respectively arranged on both main surfaces of the vibrating arms 2a and 2b, and exciting electrodes (not shown) to cause tuning fork vibration based on bending vibration are formed to these grooves 31, 32 and the vibrating arms 2a, 2b. By applying an electric current through the exciting electrodes, oscillation occurs in the quartz resonator 100.
The above-described quartz resonator is manufactured according to the following process (refer to Patent Document 1). FIGS. 8A to 8E, FIGS. 9F to 9I, and FIG. 11 are views showing the cross sectional portion along A-A′ line in FIG. 7. First, after polishing and cleaning a cutout quartz wafer 10, a metal film 11 is formed by the sputtering method (FIG. 8A). The metal film 11 consists of gold (Au) deposited on a backing film made of, for instance, chromium (Cr).
Then, after forming a resist film 12 on the surface of the metal film 11 (FIG. 8B) exposure and development processing are conducted to form a pattern having the shape of the quartz resonator 100, that is the shape of a tuning fork on the resist film 12 (FIG. 8C). Then, after it is immersed into a potassium iodide (KI) solution or the like to perform etching so that a pattern corresponding to the pattern of the resist film 12 is formed on the metal film 11, the resist film 12 is peeled off (FIG. 8D).
Next, a resist film 13 is formed on the whole surface of the quartz wafer 10 (FIG. 8E), and the resist film 13 at the parts corresponding to an opening of the pattern of the metal film 11 and the grooves 31, 32 shown in FIG. 7 is peeled off (FIG. 9F).
Thereafter, the quartz wafer 10 is immersed in hydrofluoric acid to form the outer shape of a quartz piece 17 using the metal film 11 as a mask (FIG. 9G). At this time, the quartz piece 17 is etched such that it becomes a little smaller than the outer shape of the metal film 11, which makes the end of the metal film 11 to be exposed. Next, the metal film 11 at the part corresponding to the groove 31 in FIG. 7 is etched (FIG. 9H). By this etching, the end of the metal film 11 exposed by the previously described etching of the quartz wafer 10 is etched starting from the quartz piece 17 side so as to be nearly the same size as the outer shape of the quartz piece 17. Then the quartz piece 17 is immersed in hydrofluoric acid to form the groove 31 on both main surfaces of the quartz piece 17 (FIG. 9I). Since the outer shape of the metal film 11 is formed in nearly the same dimension as that of the quartz piece 17 by the previously described etching of the metal film 11, the outer shape of the quartz piece 17 is etched a little smaller than that of the metal film 11, similarly to the etching of the quartz wafer 10 in the above-described FIG. 9G.
Though the quartz resonator 100 is manufactured according to the above-described manufacturing method, this method has the following disadvantages. The quartz resonator 100 formed in FIG. 9I is wavy at the edges of the outer shape as shown in FIG. 10, which results in appearance defect and dimensional defect. In addition, the CI value having a close relation to the outer shape of the quartz resonator 100 is also found to increase. The reason for this is considered as follows.
As described above, in FIG. 9G, the quartz wafer 10 is etched such that the end of the pattern of the metal film 11 and the end of the resist film 13 stand alone independently of the end of the quartz piece 17 (not held by the end of the quartz piece 17), as shown in FIG. 11A. Accordingly, the end of the pattern of the metal film 11 and the end of the resist film 13 are sometimes partially bent toward the quartz piece 17 side and stick to the quartz piece 17 due to the stirring of the etching solution or shaking of the quartz piece 17 as shown in FIG. 11B. Since the area of the metal film 11 coming into contact with the etching solution differs between the part where the metal film 11 and the resist film 13 are bent toward the quartz piece 17 side and the part where they stand alone toward outside of the end of the quartz piece 17 (the contact area of the former is smaller), the dimension of the metal film 11 is forced to vary at the time after etching of the metal film 11 in FIG. 9H as shown in FIG. 11C. Then, the quartz piece 17 is etched according to the outer shape of the metal film 11 in FIG. 9I. This is considered to be the reason why the outer shape line of the quartz resonator is wavy.
Patent Document 2 describes technology to form a resist film having a dimension smaller than that of a metal film formed on the quartz wafer. However, no consideration is given to the dimension defect of the above-described quartz piece.
[Patent Document 1] Japanese Patent Application Laid-open No. 2002-76806 ((0094) to (0113), FIG. 9 to FIG. 13)
[Patent Document 2] Japanese Patent Application Laid-open No. 2004-120351 ((0020) to (0023), FIG. 1 and FIG. 2)